Question

Hardness in groundwater is due to the presence of metal ions, primarily Mg2+ and Ca2+. Hardness is generally reported as ppm CaCO3. To measure water hardness, a sample of groundwater is titrated with EDTA, a chelating agent, in the presence of the indicator Eriochrome Black T, symbolized as In. Eriochrome Black T, a weaker chelating agent than EDTA, is red in the presence of Ca2+ and turns blue when Ca2+ is removed. red blue Ca(In)2+ +EDTACa(EDTA) 2+ In A 50.00 mL sample of groundwater is titrated with 0.0250 M EDTA. If 11.90 mL of EDTA is required to titrate the 50.00 mL sample, what is the hardness of the groundwater in molarity and in parts per million of CaCO, by mass? Assume that Ca2+ accounts for all of the hardness in the groundwater M CaCO hardness in molarity: hardness in parts per million: ppm CaCO

Answer 1

Selutin 5U mt amble Mae Ca2+ moles a neg EDTA = 119 x10x o.025 X - 1.1.9 x10 x 25 x 10-3 moles bf ca moles Caco 11.9 x 25 X10-6 Malanily 11.9 x 25 X10 /0 50 12 9 x2 2- 5.95 10 O.o0595 M Hardness in ppm 11.9 x25 xto 50 = 595 Fhm mas eac mass Sine ardness mass Ho 50 m 50